This invention relates to pulsed droplet deposition apparatus and more particularly to a method of operating such apparatus having a droplet liquid chamber, a nozzle communicating with said chamber for expulsion of droplets of said liquid therethrough, droplet liquid replenishment means connected with said chamber and energy pulse applying means for imparting pulses of energy to the droplet liquid in the chamber to effect droplet ejection from said nozzle. One familiar form of apparatus of the kind set forth is the drop-on-demand ink jet printer which would normally take the form of a plurality or an array of parallel ink channels having respective nozzles communicating therewith and ink replenishment means connecting the respective channels with a common ink supply.
Such drop-on-demand printers, which eject drops of fluid ink asynchronously in response to piezo-electrically or electro-thermally induced energy pulses, are known. The inks for the printers are selected to form a printed dot having high optical density and controlled spreading characteristics on the printing surface, which is typically uncoated or plain paper.
The inks which satisfy these print requirements consist typically of a solvent and ink solids including colorants, such as dyes or pigments, and possibly other additives. The ink solids may attain as much as 10-15% by weight of the ink composition and also tend to cause the ink viscosity to be enhanced substantially above that of the ink solvent alone.
When the ink viscosity is increased, the viscous impedance to flow of ink in the nozzle during pulsed drop ejection is increased, so that a higher input energy pulse is required to effect drop ejection. Accordingly it is desirable to limit ink viscosity in order to limit the operating energy or voltage. This is desirable because higher voltage requires a more expensive drive circuit or chip and, therefore, increases the manufacturing and operating cost and also reduces the reliability of the printer.